The US Food and Drug Administration (FDA) is now requiring manufacturers of testosterone supplements to include a general warning label about the risk of blood clots in the veins, various media outlets reported on Friday. While testosterone products already carry warning labels pertaining to a risk of clots associated with polycythemia, which involved an abnormal increase in red blood cells after use of such supplements, Reuters writer Esha Dey explained that the FDA has received reports of clots independent of that condition.